So just to preface things, I'm not a Christian. So I can't really speak to how well the religious aspect is articulated. But I can attest that this was a pretty crummy movie all in all.
First off this guy had an awful family to lean on. Instead of them choosing the logical option (downsizing), let's just allow our pot smoking convicted son on house arrest, who has no prior training in dealing with adults with Alzheimer's, to be dad's full time caregiver. Well that's just a quality solution. It's also sort of clever how the two young boys on riding their bicycles in cold weather found David, while no one in the three-vehicle family search party found a thing. I guess the family wasn't grateful enough to invite those two young boys to Thanksgiving dinner.
This movie could have been solved after David tried to pick up that young girl. The father who knocked him out against the lamp post should have called the cops. Roll credits.
All jokes aside, some of the dialogue between the homeless girl and David was a bit sentimental, and the "good brother" scolding the "bad brother" was a tad funny, but I can't see how any religious (or non religious person for that matter) could get a life epiphany after watching this.